Graham is easily the more interesting route because he's the more interesting character and you get the usual Fallout player-assisted character arc with him but I think Graham's role in HH gets a little misunderstood, I think because the DLC doesn't do a great job of presenting it. He's former legate of the Legion and founded the Legion alongside Caesar. His intent is killing the entirety of the White Legs, Daniel warns you of that and then when you choose his route Graham tells you to your face that's what he wants. He's the last guy you would ever want to teach someone war. And he's so dead set on this not because he actually cares strongly about the Sorrows but because the White Legs want to be part of the Legion, and he sees going against them as sort of going against the Legion by extension, basically the DLC is choosing which Mormon's baggage you want to enable. You also can draw comparisons between what Sallow/Caesar and Graham did to the tribes in Arizona by teaching them "real" war and forming the Legion out of them, and what Graham is doing to the Sorrows and Dead Horses.

Really I wish the Dead Horses and Sorrows were characterized more and that you could have actually talked to them about what they wanted to do, instead of having to deal entirely through Joshua and Daniel.